1. Field of the Invention
The present invention relates to aquatic filter systems and, more particularly, to aquatic filter systems having biological filter elements. More specifically, the invention is directed to further improvements in filter systems employing a rotary filter element composed at least in part of a body of porous material.
2. Description of Related Art
Under ideal conditions, aquatic systems including aquariums, fish ponds, and commercial fish and lobster holding tanks, will act as substantially self-contained ecosystems. That is, except for the need of the aquatic system operator to provide food to the fish within the system, the ideal aquatic system should maintain itself as an environment suitable to sustain and foster the healthy growth of the aquatic life which it contains. However, the aquatic life within the system will typically release wastes and other byproducts into the system water. In time, the buildup of undesirable wastes and pollutants can reach toxic levels and eventually poison the aquatic life within the system. As a result, it is necessary for an aquatic system to include a system for filtering and purifying the system water to eliminate undesirable wastes and toxins and to maintain a healthy environment.
Typical aquatic filters rely on mechanical filtration to remove detritus from the system water. Such a mechanical filter can be one of several types. For example, in under gravel type filtration systems for aquariums, a pump circulates the aquarium water through a bed of gravel supported on a suitable structure. The gravel bed, which is typically located within the aquarium, traps and removes solid wastes and detritus from the water as it flows through the bed. In other mechanical filtration systems, a pump removes aquarium water from the aquarium and circulates the water through a filter element and back into the aquarium. Like the gravel bed, the filter element traps and removes harmful detritus from the circulating aquarium water.
In addition to mechanical filtration, chemical filtration can be used to maintain a life-supporting environment within an aquatic system. Chemical filtration systems typically circulate the system water through a chemical filter element, such as activated carbon. This type of filtration is helpful in removing dissolved organic compounds and carbon dioxide and can help to maintain a stable pH within the aquatic system.
However, neither mechanical nor chemical filtration techniques are typically effective in removing such waste byproducts as ammonia, nitrites, or nitrates. Some of these nitrogen based contaminants, particularly ammonia, can be extremely harmful to the types of aquatic life typically found in aquatic systems. An effective method of removing such contaminants is biological filtration. Biological filtration relies on the presence of aerobic bacteria to convert some water born toxic wastes, particularly ammonia, to nontoxic or less toxic substances. It is possible for aerobic bacteria to grow, to a limited extent, on mechanical filter elements. Thus there may be some biological filtration along with the mechanical filtration described above.
However, typically, the aerobic bacteria which grows on the mechanical filter elements, or the under gravel bed, must rely on the dissolved oxygen present in the water for its growth. As a result of the limited availability of oxygen, coupled with reduced water flow as the filter becomes plugged, the amount of aerobic bacteria, and hence the degree of biological filtration, associated with mechanical filter elements or under gravel beds is inherently limited. Further, as mechanical filter elements become plugged with detritus, they must be replaced in order to maintain water flow. Each time a filter element is replaced, any aerobic bacteria which may have colonized the filter element are removed from the system and the colonization must restart on the new filter element. During the recolonization period, the environmental balance within the system may be jeopardized by the absence of sufficient amounts of aerobic bacteria.
Trickle filters have been devised as one method of fostering the growth of aerobic bacteria and increasing the efficiency of the biological filtration process. In trickle filters, water is typically removed from the aquarium, tanks or pond and allowed to trickle over a bed of lava rock, plastic balls, or the like. Because the filter bed is not submerged, there is more oxygen available for the growth of aerobic bacteria. However, trickle filters can take up a relatively large area and usually require dedicated plumbing and pump fixtures. As a result, such filters can be expensive and impractical in many applications in which a large amount of water is required to be treated.
Large scale waste water treatment facilities frequently use rotating biological contactors in an effort to promote the growth of aerobic bacteria. Rotating biological contactors typically include a number of partially submerged filter elements, frequently disc shaped, mounted along a central shaft. The central shaft is driven to rotate the elements such that at least a portion of each filter element is alternately submerged and exposed to the air. In this manner, the growth of aerobic bacteria on the surface of the filter elements is promoted by the intermittent exposure to the oxygen in the air and the biological filtration of the waste water is promoted by the intermittent submersion of the bacteria bearing surfaces. However, rotating biological contactors from waste water treatment facilities are usually not readily compatible for use with aquariums, fish holding tanks and ponds. In part, this is due to their large size, the need for a separate drive mechanism, the lack of an appropriate location for such a device within the aquarium, tank or pond, and the lowered efficiency in biological filtration when the size of the rotating biological contactors is reduced for use with aquatic systems.
Rotating biological filters which are intended primarily for use in home or office aquariums are described in copending application Ser. No. 08/004,678, filed Jan. 14, 1993, entitled "Rotating Biological Aquarium Filter System" (which is a continuation of application Ser. No. 07/535,905, filed Jun. 11, 1990) and application Ser. No. 08/004,677, filed Jan. 14, 1993, entitled "Rotating Biological Aquarium Filter System" (which is a continuation of application Ser. No. 07/708,478, filed May 31, 1991 which in turn is a continuation-in-part application of application Ser. No. 07/535,905, filed Jun. 11, 1990), the subject matter of these applications being hereby incorporated by reference in their entireties. However, these aquarium filters are not readily adapted to use in large commercial holding tanks and outdoor fish ponds.